Body Surface Area: The Mosteller Formula and Why Doctors Use It
October 29, 2026
Body surface area (BSA) estimates the total skin area of the body in square meters. Clinicians use it because many physiological quantities, such as metabolic rate, blood volume, and cardiac output, scale more closely with surface area than with weight alone. The simplest widely used formula, from Mosteller (1987), is BSA (m²) = √(height in cm × weight in kg ÷ 3,600). For a person who is 180 cm tall and weighs 80 kg: √(180 × 80 ÷ 3,600) = √4 = 2.0 m².
An average adult has a BSA of about 1.7 m², with women typically near 1.6 and men near 1.9. Newborns have about 0.25 m².
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The Mosteller formula is easy to compute by hand or on a calculator. The older DuBois and DuBois formula, BSA = 0.007184 × W^0.425 × H^0.725, gives similar results. For 175 cm and 70 kg: Mosteller gives √(175 × 70 ÷ 3,600) = 1.845 m², and DuBois gives 1.848 m². A 165 cm, 60 kg person has a BSA of 1.66 m². A 190 cm, 100 kg person has 2.30 m². Differences between the formulas are typically within 1% to 3% for adults of normal build, and larger for very small or very large people.
Use metric units: convert pounds to kilograms (divide by 2.2046) and inches to centimeters (multiply by 2.54).
| Height | Weight | BSA (Mosteller) |
|---|---|---|
| 150 cm | 50 kg | 1.44 m² |
| 165 cm | 60 kg | 1.66 m² |
| 175 cm | 70 kg | 1.85 m² |
| 180 cm | 80 kg | 2.00 m² |
| 190 cm | 100 kg | 2.30 m² |
Medical Uses
Chemotherapy doses are traditionally calculated per square meter of BSA, such as 75 mg/m², so a patient with a BSA of 1.85 m² would receive 139 mg. Cardiologists express cardiac output relative to BSA as the cardiac index (liters per minute per m²), with a normal range of about 2.5 to 4.0, to compare patients of different sizes. Burn care uses the percentage of BSA burned (the rule of nines) to guide fluid resuscitation. BSA is also used for glomerular filtration rate normalization (to 1.73 m²) and in dosing certain medications, particularly in children. Clinicians follow protocols and validated tools; this article is general information.
Limits and Alternatives
BSA formulas were derived from small samples of measured subjects and are approximations. They can be inaccurate in obesity, in very muscular people, and in children, where other formulas such as Haycock or Gehan-George are used. Some researchers argue that dosing by BSA is poorly justified for certain drugs because clearance does not scale with BSA, and use flat dosing or other methods. Capping BSA, for obese patients, remains debated. The surface area also changes if you lose or gain weight.
BSA and Metabolism
Heat loss and resting energy expenditure correlate with BSA, which is why bigger people have higher calorie needs and also why small children lose heat quickly: they have a larger surface area relative to their weight. A rough estimate of basal metabolic rate is about 35 to 40 kcal per m² per hour for adults, giving 1,500 to 1,800 kcal/day for a BSA of 1.85 m². BMR equations like Mifflin-St Jeor remain more practical for nutrition planning.
Frequently Asked Questions
What is the Mosteller formula?
BSA = square root of (height in cm × weight in kg ÷ 3,600).
What is a typical adult BSA?
About 1.6 to 1.9 m².
Why do doctors use BSA?
For dosing certain drugs and normalizing measures like cardiac output.
Is BSA accurate for obese patients?
It's less reliable, and dosing methods are debated.
How do I convert pounds and inches?
Divide pounds by 2.2046 and multiply inches by 2.54.